Dental restoration

ABSTRACT

The present invention relates to compositions and methods of use of materials in dental restoration, more specifically to the combined use of ethylenediaminotetraacetic acid (EDTA) and sodium hypochlorite to prepare a mechanically prepared tooth for crown replacement or for filling a cavity.

This is a continuation-in-part of copending application Ser. No. 003,122filed on Jan. 19, 1987 now U.S. Pat. No. 4,758,163 which is acontinuation of Ser. No. 543,314 filed Oct. 19, 1983 now U.S. Pat. No.4,645,457.

BACKGROUND OF THE INVENTION

It has previously been known that a post may be placed in anendodontically treated tooth to retain a superstructure that replacesmissing coronal tooth structure. Thus, the retention of the crown isgreatly enhanced. Posts have been employed in refabrication for severalcenturies. Over the years, posts of varying configuration have beencemented with various cements and with varying degrees of success andacceptance. Presently the two most popular cements are zinc oxyphosphatecement, which has been used since 1900, and polycarboxylate cementintroduced in 1968.

Placement of an artificial crown requires that the remaining structureof the tooth be properly prepared by instrumentation after the rootcanal space has been cleaned, shaped and filled. Generally, an interiorspace is machined into the root canal. Irrigation usually accompaniesinstrumentation and serves to cool and lubricate the cutting tool whileflushing the removed material away from the machined site. Once the rootcanal is prepared, a post of appropriate size and shape is cemented intothe canal. After the cement has sufficiently hardened, a mass around thetop of the post is built-up of various substances, to form a core.Generally, preformed crowns are available and have a hollow area toaccept such a build-up mass. These are placed as a temporary cover untila final crown has been made. This final crown is placed upon theprepared tooth structure and bonded to the tooth and core using variouscements.

In the past few years, there has been considerable discussion about theinability of chemomechanical procedures to thoroughly remove all thecellular debris within the root canal space. Silicone models are used todemonstrate the great irregularity and complexity of the root canalspace. They illustrate that even mechanically well-prepared canalsharbored areas that were never contacted by endodontic instruments.Scanning electron microscope (SEM) studies of the effects of mechanicalpreparation revealed that, regardless of the technique used, often pulptissue remained and areas of the canal walls were not instrumented. SeeMizrahi et al., "A scanning electron microscopic study of the efficacyof various endodontic instruments", J. Endod.1(10): 324-33, (1975);Moodnick et al., "Efficacy of Biomechanical instrumentation: a scanningelectron microscopic study," J. Endod. 2(9): 261-66, (1976); Bolanos andJensen, "Scanning electron microscope comparisons of the efficacy ofvarious methods of root canal preparation," J. Endod. 6(11): 815-22,(1980). In addition, other studies using the SEM found that many of thecommonly-used irrigating solutions were also ineffective in completelyremoving hard and soft tissue debris, especially in the apical portionof the canal. See Baker et al., "Scanning electron microscopic study ofthe efficacy of various irrigating solutions," J. Endod. 1(4): 127-35,(1975); McComb and Smith, "A preliminary scanning electron miscroscopicstudy of root canals after endodontic procedures," J. Endod. 1(7):238-42, (1975); Rubin et al., "The effect of istrumentation and flushingof freshly extracted teeth in endodontic therapy: a scanning electronmiscroscopic study," J. Endod. 5(11): 328-35, (1979). These results showthat the currently-accepted methods of chemomechanical preparation wereinadequate in preparing a debris-free canal.

Thus, emphasis has been placed on improving the manufacture ofendodontic instruments and developing more effective irrigationtechniques and endodontic materials.

Since instrumentation is not entirely effective in cleaning the entirecanal, the solutions used should help remove pulp tissue remnants,necrotic debris and bacteria remaining in the prepared root canal spacewithout irritating the periapical tissue.

Investigators have also described a sludge or smeared layer that existson portions of the canal walls. This appears as an amorphous layer onthe canal wall that obstructs the dentinal tubules. It was recentlydemonstrated that the smeared layer is primarily calcific in nature andis created by instrumentation. See Goldman et al., "The efficacy ofseveral Endodontic irrigation solutions: a scanning electron microscopicstudy, " Oral Surg. 52(2): 199-204, (1981).

The smeared layer blocks the dentinal tubules. A recent study has shownthat this calcific layer reduced the permeability of dentin in vitro bymore than forty percent. See Dippel et al., "Influence of the smearedlayer and intermediary base materials on the permeability of dentin," J.Dent. Res. 60(B):1211, (1981).

Therefore, even well-instrumented canals could contain organic debrissuch as pulp tissue as well as inorganic debris such as a smeared layer.Recent investigations raised the question of removing both layers. SeeWayman et al., supra and Koskinen et al., "Appearance of the chemicallytreated root canal walls in the scanning electron microscope," Scand. J.Dent. Res. 88(5):397, (1980). However, those attempts were unsuccessful.

Similarly, it has been found that the smeared layer is present in acavity and prevents an optimum bonding of the filling placed in thecavity. This permits leakage and subsequent entry of food particles andbacteria, which cause further deterioration of the tooth structure.

SUMMARY OF THE INVENTION

It has now been found that instrumented canals can be cleaned moreeffectively by using one solution to remove organic debris and anotherto remove inorganic debris. When the smeared layer is removed and thedentinal tubules are exposed, a cementing medium which has greatcompressive strength can flow into the open tubules, around the post andcan provide a greatly enhanced tensile strength and is therefore asignificant improvement over previous methods.

The present invention presents a novel solution to the aforesaidproblems by providing a method of placing a crown replacement on atooth, placing a filling in a cavity cementing of crowns and caps onnatural teeth, and filling a root canal with unfilled resin and guttapercha, which method provides enhanced foundation strength and security.The machined or prepared area is washed first with a chelating agent andthen flushed with an organic tissue solvent to remove debris and exposethe dentinal tubules. Then, in a suitable situation, the post and capare locked in place with an appropriate cementing medium. The presentinvention overcomes the disadvantages of the previous methods byproviding a method of dentinal preparation and placement thatsignificantly improves retention of coronal structures, as well aspromoting retention in other similar situations.

The invention herein comprises methods and products for attaching acrown replacement on an endodontically treated tooth. The superiorsurface of the tooth is shaped to receive the base of the crownreplacement and an interior space is machined into the root canal toaccept placement of a post. The instrumented area is then flushed with achelating agent followed by an organic solvent. A cementing mediumhaving great compressive strength is placed around a post fitted intothe cavity. After the cement has set, a quantity of filler material isplaced around the remaining exposed part of the post. This post formsthe support for the crown replacement. If desired, a preformed crownreplacement may be placed over the cemented structure until a permanentcrown can be made.

DESCRIPTION OF THE DRAWINGS

This invention can be more clearly understood by referring to theaccompanying drawings where in:

FIG. 1 is a sectional view of a damaged pre-instrumented tooth;

FIG. 2 is a sectional view of an instrumented tooth and prepared crownreplacement; and

FIG. 3 is a sectional view of an instrumented tooth having a crownreplacement.

FIG. 4 is a front elevation of a coronal post that can be used inendodontic restoration.

FIG. 5 is a vertical sectional view of a tooth having a cavity, whichtooth has been restored by use of the principles of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the present invention a tooth lacking a substantialcoronal portion is prepared for crown replacement by cleaning the rootcanal, forming a abore for placement of a post and forming a counterboreto aid in post retention. During or following instrumentation achelating agent and then an organic tissue solvent are used as a flushto prepare the instrumented surfaces for crown replacement. Followingthe surface cleaning, the post is inserted and cemented in place. A coreis formed around the post with a build-up substance and the crown isfitted in the proper position. Thus, the surface preparation by theflushing reagents aids the final placement of the crown.

In FIG. 1 of the drawing, a tooth composed of a crown area 10 and rootarea 11 is partially illustrated. The tooth, damaged and missing thecoronal portion 12, comprises dentin which surrounds the pulp cavity 1and its extension, the root canal 14. In the living tooth, the pulpcavity 13 and root canal 14 are filled with fine connective tissue whichcontains fibroblasts, histiocytes, odontoblasts, blood vessels andnerves. The oldest or primary dentin 15 lies at the periphery of thetooth and the secondary dentin 16 lies along the pulp cavity 14, whereit is formed throughout life by odontoblasts. Dentin of the crown areais covered by a thick layer of enamel 17.

A damaged tooth that has been instrumented and fitted with a preformedcoronal replacement 20 is illustrated in FIG. 2. The instrumented toothresting in gum or gingival tissue 35 comprises an instrumented coronalsurface 21, a counterbore 22, and a bore 23. The coronal replacement 20comprises the replacement shell 24, a post acceptance space 25 and aninstrumented replacement surface 26 that substantially contacts theinstrumented coronal surface 21.

A tooth having a crown replacement installed is illustrated in FIG. 3and comprises a bore 23, a counterbore 22, a threaded post 30, the apexof the thread 31 of the post, the threaded nut or fastener 32, cement ora luting agent 33, and a formed cored 34.

In accordance with the invention, a foundation of superior tensilestrength for a coronal structure is obtained by use of a chelating agentand organic solvent solution to clean the instrumented areas 22 and 23prior to cementing of a post 30. Preferably, the bore 23 and counterbore22 are rinsed with a chelating agent prior to a flush with an organicsolvent. The luting agent or cement preparation 33 is preferably placedin the bore 23, and the fitted post 30 is seated and held or supporteduntil the cement 33 solidifies. A core 34 is formed around the exposedpost 30 and fastener 32 and may be composed of the same or similarcementing medium. Other materials may be used. Following formation ofthe core 34, the crown replacement 20 is positioned in place.

in the preferred embodiment, the instrumented coronal surface 21 isformed from the damaged tooth. Then, the pulp cavity 13 (and/or the rootcanal 14, depending on the extent of work) is instrumented to form thebore 23. The depth and diameter of the bore 23 will be influenced by thesize of the pulp cavity 13 and the size of the tooth. Preferably, themajority of the root canal filling is removed to expose the dentin andprovide a suitable surface to which the cement may adhere. The finalshape of the bore is usually substantially cylindrical, however, theshape may be other shapes, such as conical or trapezoidal. Since acertain preferred dimension cannot always be obtained for the bore, thelong-term integrity of the foundation of the coronal replacement 20depends upon the adherence of the cement to the instrumented surface.

Preferably, an irrigant is used during instrumentation to aid in removalof material from the pulp cavity 15 and to lubricate the cutting toolprior to the final flush following instrumentation. Commonly usedirrigants include sodium hypochlorite (NaOCl) solution, hydrogenperoxide solution, TEGO, REDTA, RC-Prep, polyacrylic acid (20% aqueoussolution, 5000MW) and water. TEGO is a one percent solution ofdodecyldiaminoethyl glycine and is available from Goldschmidt ProductsCorporation, White Plans, N.Y. REDTA is a commercial preparationcomprising disodium ethylenediaminetetraacetate (EDTA) 17.00 gm, cetyltrimethylammonium bromide 0.84 gm, 5N sodium hydroxide solution 9.25 ml,distilled water 100 ml, and may be obtained, e.g. from Roth DrugCompany, Chicago, Ill. RC-Prep is also a commercialEDTA preparation in apaste form that is used in conjunction with sodium hypochlorite andcomprises urea peroxide 10%, EDTA 15%, a water soluble base and may beobtained from Premier Dental Products Co., Philadelphia, PA. Preferably,NaOCl is administered as the irrigant during instrumentation in anamount that removes a substantial portion of the pulp debris andlubricates the cutting tool, more preferably NaOCl is provided in asolution having a concentration of NaOCl in the range of 1% to 20%,preferably 2-10%, and most preferably in a solution having aconcentration of 4.0 to 6.0 percent NaOCl was found to be the mosteffective solution during instrumentation. All concentrations are byweight unless otherwise noted.

Following instrumentation, the bore 23 is contacted with a chelatingagent and with a solvent or dispensant for organic material. Preferably,the bore is contacted with the chelating agent prior to a flush with anorganic solvent. The purpose of the chelating agent is to substantiallyremove the instrumented or smeared layer which is primarily calcific incomposition. Suitable chelating agents include but are not limited toEDTA and citric acid. Preferably, EDTA is administered as the chelatingagent in an amount that substantially removes the smeared layer, morepreferably EDTA is provided in a solution having a concentration in therange of 1 percent to 50 percent, and most preferably in a solutionhaving a concentration of 16.0 to 18.0 percent EDTA. The chelating agentand other aqueous materials are preferably buffered to approximateneutrality, e.g. a pH of 7.5. In addition to the concentration of thechelating agent, a minimum volume of the solution must be flushedthrough the instrumented area to substantially remove the majority ofthe smeared layer. The volume of chelating agent such as 17% EDTA whichmay be administered should be sufficient to do the job, and may broadlyrange from about 1 cc to 300 cc. Preferably, less than 10 cc flush pertooth is used, and often a fluid of 2-3 cc is sufficient.

To obtain maximum effect after instrumentation, the chelating agentshould be followed by an organic solvent or dispensant. The chelatingsolutions alone effectively remove the smeared layer but leave varyingamounts of superficial debris, such as tissue and cellular componentsand possibly bacteria. Suitable organic tissue solvents include but arenot limited to, sodium hypochlorite and ampholytic soap, such as TEGO orother surface active agents, emulsifiers, etc. By "organic tissuesolvent" is meant a material which dissolves, or dispenses or otherwisechemically removes the organic debris left after instrumentation.Suitable naterials are known and described, e.g. in McCutchen'sPublications (1981), the disclosure of which is incorporated herein byreference. An ampholytic soap forms both cations and anions and thus maycombine the bactericidal activity of cations with the surface tensionreduction and solvent actions of anions. Preferably, NaOCl isadministered as the organic solvent in an amount that substantiallyremoves the superficial debris. For example, NaOCl may be provided insolution having a concentration in the range of 1% to 20%, preferablyabout 2.8%, and most preferably in a solution having a concentration ofabout 4-6%, but most preferably about 5.25% NaOCl, buffered to pH 7.5.In addition to the concentration of the organic solvent, a minimumvolume of the solution must be flushed through the instrumented area tosubstantially remove the majority of the superficial debris. If anorganic solvent such as NaOCl is administered, preferably, a volume ofNaOCl solution is provided in the range of about 1 cc to 300 cc, morepreferably 5 cc to 50 cc, and most prefereably about 8.0 to 12.0 ccflush.

Following instrumentation of the bore 23, a counterbore 22 may beinstrumented into the substance of the tooth. The purpose of thecounerbore 22 would be to provide additional area for adhesion of thecement or a mechanical lock, if shaped appropriately, once the cementhardens. Preferably, the counterbore 22 is formed at the time of theinstrumentation of the bore 23 therefore permitting administration ofthe preferred reagents as irrigant and final flushing agents in themanner described above.

Subsequently, a post 30 is fitted into the bore 23 to provide amechanical anchor for the coronal replacement 20. The post is preferablyavailable commercially as an endodontic item, more preferable it ismanufactured by any conventional process used for making such posts andmost preferably it is made of a lightweight material having sufficientcompressive strength to withstand the forces generated duringmastication and an appropriate coefficient of expansion substantiallysimilar to the companion materials employed for coronal replacement.Posts are generally cylindrical along their long axis and thereforesubstantially parallel sided, however tapered posts have also beenemployed in coronal replacement. Post retention is also influenced byshape and surface configuration, e.g., hexagonal or octogonal sides,length, diameter, and presence or absence of serrations, such asthreads. The diameter and length of the fitted post are influenced bythe size of the bore 23 and the size of the coronal replacement 20. Athreaded post may be screwed directly into the bore 23, however, thedanger of cracking the tooth is a prominent disadvantage. However,serrated posts, used in conjunction with cement, are more retentive thansmooth posts, and the surface configuration is more important thanlength. Various surface configurations, e.g., threads, serrations,convex protrusions or concave indentations, scales, etc., provide anincreased surface area on the exterior of the post. Once the cement hashardened around the post, these surface configurations, such as the apexof a thread 31, provide a significant barrier, e.g., a mechanical lock,to removal of the post from the hardened cement.

Preferably, a post with significant retentive properties such as asubstantial gripping surface for the luting agent is employed in thisinvention to provide an anchor for the coronal replacement, morepreferably the post would have significant surface configuration such asserrations, as illustrated in FIG. 3. After the post 30 is attached tothe tooth by hardened cement, a fastener 32 is screwed on or otherwiseattached to the protruding post to aid in anchoring the core 34.

In an alternative embodiment, a substantially cylindrical double-taperedpost 40 illustrated in FIG. 4 may be employed as an anchor for a coronalreplacement. The one-piece double-tapered post 40 comprises a bottomsurface 41, from which the lower tapered portion 42 extends toward themiddle section 43. The middle section 43 is necessarily of a lesserdiameter than the bottom surface 41 and divides the lower taperedportion 42 from the upper tapered portion 44 and top surface 45. Thepurpose of the lower tapered portion 42 is to provide a mechanical meansof retaining the post in the hardened cement, similar to the function ofthe threads of the post 30 of the preferred embodiment. The uppertapered portion 44 provides an anchor for the core 34 similar to thefunction of the threaded fastener 32. The one-piece double-tapered post40 would preferably be manufactured by any conventional method of alightweight material having the compression and strength characteristicsmentioned above.

Luting or cementing agents are utilized to affix the post 30 to thedentin 15 and may be used to form the core 34 as well. The strength ofthe foundation is also influenced by the type of cement employed toanchor the post. Commonly available cements for luting preparationsinclude, but are not limited to, zinc oxyphosphate, polycarboxylate,cyanoacrylate and various resins. Preferably, the luting agents employedhave substantial adhesive properties and are easily prepared andemployed in the method of the invention, more preferably the lutingagents have a high compressive strength in the range of 12,000 lb/in² to30,000 lb/in² and tend to resist the tensile and shear forces placed onthe material by mastication. Most preferably the luting mixtures ofcements have a compressive strength of at least 20,000 lbs/in². Asuitable luting agent is an unfilled resin, Bis-gamma methacrylate(Bis-GMA), combined with the catalyst therefore, which has a compressivestrength approaching 20,000-30,000 lbs /in² and which has a wateryconsistency, and flows easily with a low surface tension. Thus, theseproperties enhance its usefulness since it is easily mixed and applied.Preferably, Bis-GMA is applied in solution in a concentration that wouldprovide a compressive strength of at least 12,000 lbs/in2, morepreferably at least 20,000 lbs/in² and most preferably approximately30,000 lbs/in².

Once the post 30 has been fitted to the tooth, a quantity of cement 33sufficient to contact the dentin 15 and the fitted post 30 is depositedin the bore 23. The length of the post is adjusted during fitting sothat a portion of the post protrudes from the bore. Once the post isanchored in the hardened cement, the threaded fastener 32 is rotatablyattached to the protruding part of the post 30. The threaded fastener 32is preferably made of a lightweight material having a compressivestrength similar to that of the post 30. The purpose of the threadedfastener 32 is to provide a prominent surface around which a core 34 maybe formed. This prominent surface and the counterbore may be usedtogether to provide a mechanical means of retaining the core 34 once ithas hardened.

The core 34 may be composed of a composite, cement or luting agentsimilar to the core cement, or a different substance, such as amalgam.Preferably, the core 34 should be composed of a material havingsufficient bonding and compressive strength to withstand the pressuresencountered. In addition, the core substance must have substantialmechanical and/or chemical affinity for the coronal replacement 20.

The coronal replacement 20 is preferably performed by any manufacturingprocess used in molding crowns, and comprises a replacement shell 24 anda post acceptance space 25. During the fitting procedure the coronalreplacement 20 is substantially shaped to create an instrumentedreplcement suface 26 which conforms to the contours of the instrumentedcoronal surface 21. Once the coronal replacement 20 has been fitted tothe tooth, a core 34 is formed around the threaded fastener 32 and post30 providing an amount of core substance to substantially fill thecounterbore 22 and post acceptance space 25 of the coronal replacement20.

Although not wishing to be bound by theory as to why the structureprepared by this invention reduces the possibility of loosening, it isbelieved that when the organic debris and the smeared layer are removedfrom the machined bore 23 and counterbore 22, the dentinal tubules areexposed. The most effective final flush after instrumentation was foundto be 10 cc of 17 percent EDTA followed by 10 cc of 5.25 percent NaOCl.The best result is obtained when a 5.25 percent solution of NaOCl isemployed during instrumentation to lubricate and remove the majority ofthe pulp debris. Thus, a cementing medium which has great compressivestrength, such as bis-GMA resin, can flow into the open tubules and intothe serrations of the post and provide greatly enhanced tensilestrength.

The following examples are set forth to further illustrate the presentinvention.

PREPARATION AND ANALYSIS OF MATERIALS

One hundred and twenty freshly extracted singly-rooted teeth wereselected. The crowns were removed at the cervical line and a postpreparation either 4 mm or 7 mm was made with the appropriately sizedburr to receive a 0.050 parapost (Whaledent Corp.). The teeth were thendivided into two groups of 60 teeth each. Each group was furthersubdivided into two groups, each of which had 30 teeth with 4 mmpreparations and 30 teeth with 7 mm preparations.

In Group A, all the post preparations were flushed with a syringe and 23gauge needle using 2 cc of 5.25% NaOCl and the canals were dried withpaper points and air. In Group B, all the post preparations were flushedwith a syringe and 23 gauge needle using 1 cc of 17% EDTA solutionfollowed by 1 cc of 5.25% NaOCl after which the canals were dried witypaper points and air. Both groups were then divided into three subgroups(Table I).

Group A - all teeth flushed with 2 cc of 5.25% NaOCl and dried with anair blast and paper points.

Group A 1--Zinc oxyphosphate cement powder and liquid were dispensedonto the clean, dry surface of a glass slab and carefully mixedaccording to manufacturer's directions to a creamy consistency suitablefor cementation. A lentulo spiral was used to place the cement in eachpost preparation. The post was then coated with the cement and seated toplace and held until initial setting occurred.

Group A 2--Polycarboxylate cement powder and liquid (Durelon-Premier)were dispensed onto a clean dry slab and carefully mixed according tomanufacturer's directions to a creamy consistency. A lentulo spiral in asuitable handpiece was used to place the cement in the post preparation.The post was coated with the cement and seated to place and held untilinitial setting occurred.

Group A 3--A 30% mixture of Bis-GMA resin with the catalyst, TEGDMA, wasdispensed onto a paper mixing pad, the catalyst added and mixed. Alentulo spiral by hand was used to place the resin in post preparationuntil it was completely coated. Resin was used to coat the post whichwas seated and held until initial set.

Group B - all teeth were flushed with 1 cc of 17% EDTA followed by 1 ccof 5.25% NaOCl and then dried with an air blast followed by paperpoints.

Group B 1--Posts cemented with zinc oxyphosphate cement and sameprocedure as Group A 1.

Group B 2--Posts cemented with polycarboxylate cement and same procedureas Group A 2.

Group B 3--Posts cemented with unfilled Bis-GMA resin and same procedureas Group A3.

After cementation, all teeth were stored in 100% humidity at roomtemperature for at least one week before testing.

The teeth were then tested for tensile strength on an Instron testingmachine at a cross head speed of 0.1 in/min.. The tensile strength ofthe post was tested to failure.

The results were statistically analyzed using a 3-dimensional factorialanalysis of variance. Results were obtained for 114 teeth. The tensilestrengths are summarized in Table I.

Without wishing to be bound by theory, it is believed that theimprovement obtained by use of the particular solvent combination,removes both the organic and inorganic debris, and thus eradicates thesmeared layer which would otherwise overlay the tubules. When this layerhas been removed, a light, low-viscosity, low-surface tension cement(such as unfilled gamma methacrylate) can penetrate these pores, thus toestablish a mechanical seal in which the cured resin protrudes into thepores and sets up a mechanical lock inside the tubules. The strength ofthis bond is believed to be such that bond failure generally occurswithin the adhesive itself, rather than to the interface.

                  TABLE I                                                         ______________________________________                                        RELATIVE TENSILE STRENGTH OF                                                  POSTS USING DIFFERENT BINDING                                                 AGENTS AND DIFFERENT RESINS                                                                           EDTA                                                                          &       Recent                                        Group I - 4mm. Posts                                                                        NaOCl     NaOCl   Improvement                                   ______________________________________                                        Zinc Phosphate                                                                              37.59     52.73   clcl                                          Polycarboxylate                                                                             29.03     40.05   38%                                           Resin         51.55     97.40   89%                                           Group II - 7 mm. Posts                                                        Zinc phosphate                                                                              51.31     63.40   24%                                           Polycarboxylate                                                                             41.55     46.37   12%                                           Resin         55.00     124.00  126%                                          ______________________________________                                    

The very clear cut superiority of the posts cemented with bis-GMA resinfollowing an EDTA-NaOCl flush was indisputable. As shown in Title I, itwas significantly better in every case and under every circumstance. Thestrongest post in the zinc phosphate group was the 7 mm one followingthe EDTA-NaOCl rinse. The 4 mm post cemented with bis-GMA after anEDTA-NaOCl rinse had an 89% improvement in tensile strength, as comparedwith the same post and resin, but utilizing only an NaOCl resin. The 7mm post cemented with bis-GMA after an EDTA-NaOCl rinse had more thantwice the tensile strength. The strongest post in the polycarboxylategroup was the 7 mm one cemented after an EDTA-NaOCl flush and here the 4mm bis-GMA post was twice as strong and the 7 mm bis-GMA post was threetimes as strong.

These results indicate that when the smeared layer is removed and thedentinal tubules are exposed, a cementing medium which has greatcompressive strength such as the bis-GMA resin which is not soluble inthe oral fluids, can flow into the open tubules on the one side and intothe serrations of the post on the other side can provide a greatlyenhanced tensile strength.

An important aspect of this technique lies also in the fact that since a4 mm post cement with the unfilled bis-GMA following an EDTA-NaOClrinse, can have one and a half times the tensile strength of the best 7mm post cemented with zinc phosphate, shorter posts can and should beused. These are much easier to prepare and inadvertant perforations ofthe side of slender or curved roots would be much less likely to occur.If a longer post is chosen, then the 7 mm post cemented with unfilledresin after an EDTA-NaOCl rinse has tensile strength equalling or atleast approaching the tensile strength of known screw-in posts. Thisallows a simpler procedure without the danger of cracking the root whichis inherent with the screw-in post.

When the invention is used to provide a foundation for a coronalstructure, the danger of the core loosening or being damaged due to thetremendous pressure encountered by the dental structure is significantlyreduced. Reduction of loosening problems will be effected by using anypreparation in accord with the invention have a prepared dental areaflushed by a chelating agent followed by an organic solvent and a lutingagent of high compressive strength employed to anchor a post insertedtherein for a coronal structure.

FIG. 5 is a cross-sectional view of a tooth 100 shown as a molar thathas been restored in accordance with the teachings of the presentinvention. The tooth has a crown 101, a neck 102, and roots 103.Extending around the outer periphery is a layer of enamel 111.Immediately within the enamel is the dentin 112. Centrally of the toothis the pulp chamber 113. The outer surface of the roots 103 are providedwith cementation and the crown is shown as provided with cementation andthe crown is shown as projecting above the gum 115.

The tooth is shown as having a cavity 116 which has been provided with afilling 17 of bis-GMA resin and an amalgam 118.

The method used for restoring the tooth 100 is very similar to themethod used to produce the post and crown restoration of FIG. 3. Themethod consists of mechanically preparing the tooth to receive thefilling, including cleaning debris from the cavity 116 and possiblyundercutting. The prepared area is then flushed with a chelating agentselected from the group consisting of citric acid andethylenediaminetetraacetic acid and then flushing the prepared area witha solvent selected from the group consisting of sodium hypochlorite,surface active agents and emulsifiers. The solvent dissolves, dispensesor otherwise chemically removes organic debris. Then a low-viscosityluting agent is provided in the cavity and later placing the filler 117is inserted in place, contacting the filler and the dentin of the toothwith the luting agent. The filler is allowed to harden and the amalgamis inserted in the remainder of the cavity and is faired to the toothsurface.

Since it has been difficult in the past to bond to the dentin (ascontrasted with bonding to the enamel), the present system solves along-standing problem. In the past, using traditional methods, a bondingstrength of 400 psi was considered optimum; with the present method ithas been possible to obtain bonding strengths 1600-1800 psi. Apparently,the technique of the invention acts to remove the smear layer from thedentin and expose the tubules to access by the low-viscosity cement. Thesmeared layer is very tenacious, since it consists of a very greasycombination of inorganic and organic elements. The present inventivemethod is very mild and does not affect the remaining calcified tissue.The method is particularly effective in situations in dental restorationwhere bonding must take place almost entirely with dentin and whereenamel is not available to support the restoration materials.

The procedures described above can be effectively used in connectionwith the cementation of crowns and caps on natural teeth, particularlyin situations where the cap is in contact with the dentin. In this case,the outer layer of enamel and some dentin is removed, to provide roomfor the crown. After this removal, the dental surface is washedthoroughly in accordance with the invention as described above; then,the surface is dried carefully and a thin layer of a bis-GMAlow-viscosity unpolymerized resin (containing its own catalyst) ispainted over the entire surface of the prepared tooth. This is allowedto polymerize and an impression is made to permit preparation of thecrown. Once prepared, the crown is then cemented to the prepared surfacewith a bis-GMA cement; this provides a strong chemical and mechanicalbond which prevents marginal micro-leakage and prevents bacterialpenetration. A similar situation exists in filling an instrumented rootcanal; the tubules in the dentin are exposed by the process of theinvention and a low-viscosity unfilled resin is used. The resin entersthe tubules and the pre-fitted gutta percha point is inserted. This actsas a pressure medium to force the resin into the tubules and otherirregularities in the surface of the canal. The resin then polymerizesunder the action of its contained catalyst; thus creating a filling ofany gaps between the gutta percha and the canal surface. This preventsmicro-leakage and the entry of bacteria.

Obviously minor changes may be made in the form and construction of thisinvention without departing from its spirit. Thus, it is not desired toconfine the invention to the exact form shown and described, but it isdesired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:

We claim:
 1. Method for restoring a tooth comprising: preparing thetooth to accept a prosthesis, preparing the tooth to accept a filling,flushing said prepared area with a chelating agent selected from thegroup consisting of citric acid and ethylenediaminetetraacetic acid,then flushing said prepared area with a solvent selected from the groupconsisting of sodum hypochlorite, surface active agents and emulsifiers,which solvent dissolves, dispenses or otherwise chemically removesorganic debris, placing a low-viscosity luting agent in said preparedarea, placing said filling in said prepared area, contacting saidfilling and the dentin of the tooth with a low-viscosity luting agent,forming finish structure around the exposed filling, and installing thefinish structure.
 2. Method of claim 1 wherein said chelating agent isethylenediaminetetraacetic acid.
 3. Method of claim 1 wherein saidorganic solvent is sodium hypochlorite.
 4. Method of claim 2 whereinsaid chelating agent comprises about 1 to 50% by weight ofethylenediaminetetraacetic acid.
 5. Method of claim 2 wherein thechelating agent comprises about 10 to 16% by weight ofethylenediaminetetraacetic acid.
 6. Method of claim 3 wherein said(organic) solvent is about 1 to 20% by weight sodium hydrochlorite. 7.Method of claim 3 wherein said (organic) solvent is about 4-6% by weightof sodium hypocholrite.
 8. Method of claim 1 wherein said fillingcomprises insulating material.
 9. Method of claim 1 wherein said lutingagent is Bis-GMA resin.
 10. Method of claim 1 wherein said preparationis accompanied by flushing with an irrigation solution.
 11. Method ofclaim 10 wherein said irrigation solution is an organic solvent. 12.Method of using a restoration filler material that comprises preparingthe area of a tooth, flushing said prepared area with a chelating agentselected from the group consisting of citric acid andethylenediaminetetraacetic acid followed by a solvent selected from thegroup consisting of sodium hypochlorite surface, active agents andemulsifiers which dissolves, dispenses or otherwise chemically removesorganic debris, and placing said filler material in said flushed area.13. Method of restoring a tooth having a caries cavity, comprising:(a)mechanically cleaning the surface of the cavity (b) flushing saidcleaned surface with a chelating agent followed by an organic solvent,and placing filler material in said flushed area.
 14. Method of claim13, wherein said filler material is Bis-GMA.